The reason I suggested lugging was because your description of the car jerking reminds me of times when I have accidentally driven a car (or motorcycle) at low enough revs to where it is bucking a little.  The fact that it only happens in 2nd is curious.  Are we sure it doesn't act like that at low rpm in 3rd and 4th for instance?
				
			 
	 
 
		 
 
		 
 
		 
 
		

